A significant proportion (42 percent) of HIV infections remain linked to unprotected sex between men who have sex with men (MSM). In 1998 over half (51 percent) of all AIDS cases reported among young males between the ages of 13 and 24 years old were attributed to unprotected sex with other males. Furthermore, studies published this year on the prevalence of HIV infection in young MSM found that on average 7 percent of their young MSM samples in seven major U.S. cities were infected with HIV. More than two decades into the AIDS epidemic, MSM still clearly remain at high risk for HIV infection, in spite of the large-scale intervention efforts underway to prevent HIV. This situation underscores the need for more model-based research to examine potential predictors of unprotected sex in MSM. This dissertation will develop model-based questionnaires in a sample of 250 sexually active young adult MSM and then conduct confirmatory and predictive analyses with an additional sample of 250 sexually active young adult MSM. The measures will be based on two important behavior change models including the Transtheoretical Model of behavior change (TTM) and the Multifaceted Model of HIV Risk. Due to the inherently interpersonal nature of condom use, interpersonal and contextual variables will be examined by adapting scales assessing sexual assertiveness, sexual experience, negotiation styles, and anticipated partner reactions for MSM. Internalized homophobia will also be examined as a possible predictor of unprotected anal sex. These measures, in addition to the TTM-based constructs, could provide an explanatory advantage to increase our understanding of condom readiness in MSM for both insertive and receptive anal sex. Exploratory cross-sectional studies like this are needed to validate specific theory-based measures such as TTM-based measures within samples of MSM. Doing so could strengthen the foundation for augmenting current and future large-scale theory-based interventions with MSM.